Messages in this thread | | | Date | Tue, 15 Oct 2013 14:59:15 +0200 | From | Frederic Weisbecker <> | Subject | Re: Panic and page fault in loop during handling NMI backtrace handler |
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On Tue, Oct 15, 2013 at 05:48:37AM -0700, Paul E. McKenney wrote: > On Tue, Oct 15, 2013 at 02:37:17PM +0200, Peter Zijlstra wrote: > > On Tue, Oct 15, 2013 at 02:18:53PM +0200, Frederic Weisbecker wrote: > > > On Tue, Oct 15, 2013 at 02:01:04AM +0000, Liu, Chuansheng wrote: > > > > We meet one issue that during trigger all CPU backtrace, but during in the NMI handler arch_trigger_all_cpu_backtrace_handler, > > > > It hit the PAGE fault, then PAGE fault is in loop, at last the thread stack overflow, and system panic. > > > > > > > > Anyone can give some help? Thanks. > > > > > > Looks like we re-enter the fault several times. On x86-32, NMIs can > > > fault if they dereference vmalloc'ed area. I wonder if the module thing > > > we lookup in the NMI is stored on some vmalloc'ed area. > > > > IIRC modules are indeed allocated using vmalloc. See module_alloc() > > using vmalloc_exec() > > This might then be a module that uses call_rcu(), but which does not have > the needed rcu_barrier() in the module-exit function.
I rather believe it's due to the lazy paging of vmalloc area in x86-32. We had issues like that in the past. For example that's the reason why we do an ad-hoc per-cpu allocation on callchain buffers in perf rather than using alloc_percpu() which might use vmalloc.
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